Star data network with logical ring function preferably using token access

ABSTRACT

Star data network with logical ring function preferably utilizing token access, including a line concentrator with a plurality of bypass switches each arranged for its respective link in a node in the data network. Each bypass switch in the concentrators is provided with a preferably active signal processing element adapted on one signal side for superimposing an incoming and outgoing signal on the same transmission line in the link and on its other side for smoothing out the incoming signals contribution to the outgoing signal, and in that the transmission line in the link is connected to the node via a preferably passive signal processing element with a function corresponding of the function of the preferably active signal processing element, the transmission line preferably being a coaxial cable installed in an earlier terminal network.

TECHNICAL FIELD

The invention relates to a star data network with logical ring functionpreferably utilizing token access.

BACKGROUND ART

Star data networks with logical ring function utilizing token accesshave been well known for ten years. An exhaustive description of theconcept and its realization with the aid of line concentrators waspublished in 1983 in IBM systems Journal vol 22, nos 1/2, by R. C.Dixon, N. C. Strole and J. D. Markow.

Embodiments known up to now of data network with logical ring functionusually have the disadvantage of requiring new lines for achievingsatisfactory function. This means that large earlier investments interminal networks with coaxial cables cannot be utilized in suchembodiments.

DISCLOSURE OF THE INVENTION

The invention relates to a star data network with token access realizedin such a way that use can be made of earlier investments in terminalnetworks with coaxial cables.

In addition, the invention enables the utilization of simpler and lessvoluminous connector means than what is indicated in the specificationISO/DIS 8802/5 for data networks according to the above.

In accordance with the invention this is achieved by a conventional lineconcentrator, with a plurality of bypass switching means each arrangedfor its respective link to a node in the data network, having each ofthe mentioned bypass switching means provided with a preferably activesignal processing means disposed such as to superimpose on one signalside an incoming and an outgoing signal on the same transmission line insaid link, and on its other signal side to smooth the incoming signal'scontribution to the outgoing signal, and in that said transmission linein said link is connected to said node via a preferably passive signalprocessing means with a function corresponding to the function of saidpreferably active signal processing means, said transmission linepreferably comprising a coaxial cable installed in an earlier terminalnetwork. In a preferred embodiment in accordance with the invention ofthe preferably active signal processing means, the latter includes anamplifying comparator with a reference input adapted for having suppliedto it the incoming signal via a first attenuation circuit and with asignal input connected to said transmission line, which is adapted forbeing supplied with the incoming signal via a second attenuation circuitcorresponding to the first attenuation circuit.

DESCRIPTION OF FIGURES

FIG. 1 is a block diagram of a star data network with logical ringfunction.

FIGS. 2 and 3 are circuit diagrams of preferred embodiments inaccordance with the invention of an active and passive signal processingmeans, respectively.

FIG. 4 is a perspective view of a preferred embodiment of an adapter inaccordance with the invention, in which the passive signal processingmeans according to FIG. 3 is included.

BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 is a block diagram illustrating a conventional star data networkwith logical ring function, including a first line concentrator 1having, according to the example, three bypass switching means 2, 3, and4 each arranged for a link 5, 6 and 7 to nodes 8, 9 and 10, and a secondline concentrator 11 with bypass switching means 12, 13 and 14 eacharranged for links 15, 16 and 17 to nodes 18, 19 and 20 in the datanetwork. The two line concentrators are connected together by a link 23and bypass switching means 21 and 22.

A more detailed description of the function of the data network in FIG.1, utilizing token access is published in IBM Systems Journal vol 22,nos 1/2, 1983 by R. C. Dixon, N. C. Strole and J. D. Markov.

Embodiments known so far of data networks with logical ring functionutilizing token access have the disadvantage of requiring new lines forachieving satisfactory function. The specification IEEE 802.5 / ISO/DIS8802/5 has been prepared for ensuring the function.

In accordance with the invention, satisfactory function in the datanetwork according to FIG. 1 and compatibility with the above mentionedspecification IEE 802.5 / ISO/DIS 8802/5 can be achieved while makinguse of earlier investments in terminal networks with coaxial cable withthe aid of the following arrangement: the combination that each of thementioned bypass switching means 2, 3, 3, 12, 13 and 14 in the mentionedline concentrators 1 and 11 is provided with a preferably active signalprocessing means arranged on one signal side to superimpose an incomingand an outgoing signal on the same transmission line in said link, andon its other signal side to smooth the incoming signal's contribution tothe outgoing signal, and that said transmission line in said link isconnected to said node via a preferably passive signal processing meanswith a function corresponding to the function of said preferably activesignal processing means, said transmission line preferably being acoaxial cable installed in an earlier terminal network.

FIG. 2 is a circuit diagram of a preferred embodiment in accordance withthe invention of said preferably active signal processing means 24 insaid line concentrators 1 and 11, said bypass switching means includinga contact means 25 operated by a relay coil 26 driven by a transistorstep 27 via an optocoupler 28 from a coaxial line 29 connected to one ofsaid nodes in the data network.

The signal processing means 24 is connected for signalling to thecoaxial cable 29 via a wideband transformer 38. The chief function ofthe transformer is to heavily supress longitudinal interference possiblyoccurring in the coaxial network.

Operation of the respective bypass switching means 25 takes place withthe aid of a direct voltage generated at the respective node in thecoaxial network, see FIG. 3. The bypass switching means is activated bythe node sending a positive signal on the input 40, 41 relative theoutput 42, 43. The direct voltage is applied to the coaxial cable 44 viathe resistors 45, 46 and 47. In order to detect the direct voltage atthe other end of the link, see FIG. 2, independent of possiblelongitudinal interference, an optocoupler 28 is used, connected inseries with a resistor 36 to the incoming coaxial cable 29. The directvoltage activates the optocoupler 28, the output of which drives thetransistor step 27, which gives the necessary drive current to the relaywinding 26, which causes the relay contacts 25 to switch. The seriesresistor 36, which is grounded via the capacitor 39 for signalling,reduces the action of the optocoupler on the impedance at the coaxialinterface.

The impedances in the coaxial contacts 29 and 44 must be adjusted to thecharacteristic impedance (in this case 93 ohms) of the coaxial cable sothat the signal quality is not deteriorated by reflections at the endpoints of the link. In FIG. 2, the buffer amplifier 37 has a low outputimpedance, while the amplifier 30 has high input impedance. Theimpedance at the coaxial interface 29, within the frequency band inquestion, mainly comprises the sum of the resistance 35 and the bufferamplifier output impedance in parallel with the resistance 36, whichgives good adaptability to 93 ohms. Corresponding impedance adjustmentis necessary at the other end of the respective link and is provided bythe passive signal processing means according to FIG. 3, with the aid ofthe resistors 45, 46, 48 and 49 in combination with the impedances whichare connected between 40 and 41 and 42 and 43, respectively, being 150ohms.

Separation of the input and output signals superimposed in the coaxialcontact 29 takes place, as illustrated in FIG. 2, with the aid of thecomparing amplifier 30, which can suitably be implemented as adifferential step with the voltage gain 12 dB. The incoming signal isapplied to the amplifier 30 via a first attenuation circuit 32 , 33 andalso via a second attenuation circuit, which comprises the resistor 35in series with an impedance comprising that of the coaxial cable (93ohms) in parallel with the resistor 36. By selecting the attenuation thesame in these two circuits the incoming signal will give rise to anequally as great signal on both inputs 31 and 34, and thus will not giveany contribution to the output signal. In FIG. 3 the separation of bothsuperimposed signals takes place with the aid of passive components. Theinput signal is allowed to pass the wideband transformer 50 and issubsequently divided up into two equally as large impedances, of whichone is the coaxial cable impedance (93 ohms) in parallel with theresistor 45, and the other is the resistor 48. Due to the symmetricimplementation it will be understood that the input signal will not giveany contribution at the central output 51 of the transformer, the output42 being connected to this central output 51. The resistor 49 has thetask of improving adaption to the output 42, 43.

The inversion of the output signal which the amplifier 30 causes isrighted for each link by the corresponding inversion in the windebandtransformer 50 of the incoming signal in the passive signal processingmeans at the other end of the link.

FIG. 4 illustrates a mechnical implementation where the passive signalprocessing means 53 has been fitted into a standard screening casing 55of a 9-pole D-sub device 56 and where the coaxial connection takes placedirectly to a BNC-contact 54 mounted in the screening casing.

We claim:
 1. Star data network with logical ring function utilizingtoken access, including line concentrators with a plurality of bypassswitching means each arranged for a corresponding link to a node in thedata network, wherein each of said links comprises at least onetransmission line, and wherein each of said bypass switching means isprovided with an active signal processing means having first and secondsignal sides, said active signal processing means being adapted forsuperimposing on said first signal side a first incoming and a firstoutgoing signal on a single transmission line in said correspondinglink, and on said second signal side for smoothing out a second incomingsignal's contribution to a second outgoing signal, said first incomingand first outgoing signals on said first signal side corresponding tosaid second outgoing and second incoming signals on said second signalside, respectively, said single transmission line in said correspondinglink being connected to said node via another signal processing meanswith a function corresponding to the function of said active signalprocessing means.
 2. A data network as claimed in claim 1, wherein saidbypass switching means is adapted for operation with the aid of anelectric signal from said node over said at least one transmission lineof said link.
 3. A star data network as claimed in claim 1, wherein saidactive signal processing means includes an amplifying comparison meanswith an output for said second outgoing signal on said second signalside, with a reference input to which is supplied said second incomingsignal on said second signal side via a first attenuation circuit, andwith a signal input connected to said single transmission line, thesingle transmission line being arranged on said first signal side forsupplying to said signal input said first incoming signal via a secondattenuation circuit which is matched to provide substantially the sameattenuation as said first attenuation circuit so as to smooth out saidsecond incoming signal's contribution to said second outgoing signal onsaid second signal side.
 4. A star data network as claimed in claim 1,wherein said at least one transmission line comprises a coaxial cableinstalled in an earlier terminal network.
 5. A star data network asclaimed in claim 1, wherein said other signal processing means comprisesa passive signal processing means.